A wheelchair seat cushion must perform a number of important functions. The seat cushion should be comfortable and capable of providing proper support for optimal posture and posture control for a considerable length of time. The seat cushion should also assist, or at least not materially hinder, the user in maneuvering the wheelchair, permit a useful range of motion from the pelvis and upper torso of the person, and create stability and security for the person within the wheelchair. Perhaps most importantly, the seat cushion should help prevent and reduce the incidence of pressure ulcers created by prolonged sitting on the cushion without adequate pressure relief. Pressure ulcers can become a very serious health problem for individuals who must remain constantly in contact with the support cushion, and it is important to avoid such pressure ulcers.
Wheelchair users are of substantially different sizes, weights and shapes. Many wheelchair users have physical disabilities and associated posture and postural control impairments such as those typically caused by congenital disorders. Other wheelchair users, such as those who have been disabled by acquired or traumatic injuries, may have a more typical size and shape. In all of these cases, the support contour of the wheelchair seat cushion must safely support the anatomy of the user, whether the anatomy is abnormal or more typical. Wheelchair seat cushions must fit and perform properly to prevent further physical impairment and pressure ulcers. The cushion must also enhance the functional capabilities of the user by supporting independence in activities of daily living. There are a number of different theories or approaches for configuring the support contour of a wheelchair seat cushion to avoid pressure ulcers and to provide adequate postural alignment.
One approach to configuring the support contour of a wheelchair seat cushion is a single generic support contour which attempts to accommodate all types of pelvic bone-structure configurations, whether more abnormal or more typical. In general, this generic approach involves using a soft, flowable or adaptable material, such as air or gel, as the support material within the wheelchair cushion. This adaptable material adjusts and redistributes in response to the weight and shape of the user to create a support contour which conforms to the anatomy of the user. By conforming to the anatomy of the user, the pressure on the skin of the user is usually distributed relatively evenly over the area of contact. The extent of the uniform pressure distribution depends on the capability of the cushion to accept and conform to the user's anatomy without displacing the adaptable material and resulting in firm contact with a support structure.
The substantially equal pressure distribution is theorized to reduce the incidence of pressure ulcers, by decreasing peak pressures on the skin in the pelvic area associated with bony prominences, most notably the ischial tuberosities, coccyx, sacrum, and greater trochanters. However, as individuals age with their disabilities, the quality of their skin is further compromised in its ability to tolerate pressure and shear forces. The decreased tolerance for pressure and shear forces, no matter how well those forces are distributed, increases the incidence of pressure ulcers.
Generic seat cushions which use flowable support material are usually incapable of providing adequate postural alignment. In general terms, adequate postural alignment is assisted by using the support contour of the seat cushion to encourage proper posture by providing a foundation for dynamic posture control. To do so, the support contour must have the capability of applying some support pressure to the pelvic area because alignment of the pelvic area is fundamental for proper posture. The adaptable support material of generic seat cushions is intended to move and redistribute itself, and consequently, is generally unstable and incapable of applying the support pressure or force in certain areas of the pelvic anatomy to optimize postural control and alignment.
Many of the disadvantages associated with generic wheelchair cushions may be overcome by using a custom wheelchair seat cushion having a support contour constructed specifically to accommodate the individual anatomical aspects of a particular user. In such cases, it is necessary to capture the anatomical shape of the individual which will contact the custom seat cushion, and then use that anatomical shape to make the custom seat cushion.
The cost of fabricating a custom wheelchair seat cushion can be substantial, for example, approximately $3000 or more. Much of the expense of a custom wheelchair seat cushion results from the amount of time consumed, and the cost of the relatively sophisticated equipment which must be used to capture and transfer the anatomical shape of the user into the support contour of the seat cushion. Moreover, despite the use of sophisticated equipment, it is nevertheless difficult to capture the anatomical shape of the user and transfer it into a customized support contour. An appreciation of some of these difficulties in creating customized wheelchair seat cushions is discussed in the above-referenced U.S. patent application Ser. No. 10/628,858.
The most prevalent approach used to configure the support contour of a custom cushion, at least at the time of filing hereof, is to distribute the weight of the user substantially uniformly over the entire support contour. The uniform pressure distribution is theorized to reduce the incidence of pressure ulcers because the uniform pressure distribution is thought to avoid localized high-pressure points which could give rise to pressure ulcers. The substantial conformance of the support contour to the anatomical shape of the user is also believed to orient the user toward proper postural alignment.
Even if the support contour of the custom cushion is initially satisfactory to the user, changes in tissue and musculature may dictate changes in the optimal support contour of the custom seat cushion. Tissue will typically atrophy over time, particularly for first-time wheelchair users. Tissue atrophy and other tissue changes alter the pressure distribution over the support contour. Those changes may result in increased pressure on tissues surrounding the bony prominences, thereby ultimately increasing the risks of pressure ulcers. Moreover, as the muscle strength diminishes, the user relies more on the support contour of the seat to hold the proper posture. In doing so, parts of the pelvic anatomy press more directly on certain parts of the support contour as a foundation for postural alignment. The increased pressure from postural alignment increases the pressure and shear forces on the skin in those areas, again increasing the risk of pressure ulcers. In general, the concept of equally distributing the pressure over the entire support contour of the custom seat cushion is generally obtainable only for a limited amount of time and under limited circumstances. Additionally, any movement of the user, or even subtle changes in pelvic orientation on the support contour, can result in substantial increases in pressure and shear forces on the skin at the interface with the support contour.
One type of existing wheelchair cushion includes a cutout area adjacent to the tailbone or sacrum in the pelvic area. This cutout area is effective in eliminating pressure or shear forces which could cause pressure ulcers on the skin surrounding the sacrum. However, the single cutout area does not address the increased pressure and shear forces which occur at the areas of other bony prominences in the pelvic area. Moreover, the support contour of the cushion with the cutout area does not attempt to transfer support to other pelvic areas to compensate for the reduced support at the cutout area. This type of cushion is not generally intended to encourage or bias the pelvic area into alignment for proper posture. Instead, this type of cushion is intended to be used with a separate back support cushion in order to invoke postural alignment.
Many of the same considerations applicable to wheelchair seat cushions also apply with varying levels of criticality to other types of seat cushions used in other seating environments and applications. For example, seat cushions used in office environments are required to support the user in a comfortable manner which encourages proper posture and without creating risks of medical problems, for example inducing blood circulatory problems.